Doing Titrations Flashcards
what is a titration
- a practical method of measuring the volumes of two solutions that react together
- and then using that information to calculate the concentration of one of the solutions
what is a base that is soluble in water called
an alkali
why do we use indicators in a titration which change the colour of the solution depending on whether it is acidic, alkali or neutral
- because all the acids and alkalis as well as the products made from them reacting are colourless
- meaning that you would need an indicator to visually know when the reaction is complete
what is the summarised method of a titration
- add the acid to the alkali until the equivalence point of the titration and end point of the indicator is reached
- record the lowest part of the meniscus
- record the titre
- repeat until concordant titres are obtained
what is a meniscus
the lowest part of the solution level in the burette if a concave shape is formed
what are the common apparatus used in a titration
- a conical flask
- a burette and stand
- a pipette and pipette filler
- a white tile
- a small funnel
- a wash bottle containing deionised water
what is the very first step of a titration
- rinse the conical flask with deionised water
- place on a white tile
what is the second step of a titration
- use a pipette filler to rinse the pipette with deionised water
- then fill with sodium hydroxide solution
what do you do after the pipette has been rinsed
you use the pipette to transfer a known volume of sodium hydroxide solution into a conical flask
what is then added into the conical flask
2 to 3 drops of an indicator (methyl orange or phenolphthalein)
what is then done to the burette after this
- it is rinsed with deionised water
- and filled with the acid solution
- to be set up in the stand above the conical flask
after you record the reading on the burette taking the meniscus into consideration, what is the important part of this titration
- adding the acid solution into the conical flask until it just changes colour
- in which you would then record the reading on the burette again
what is the final step in order to get concordant titres
- empty the conical flask and rinse it with deionised water
- then repeat the experiment again
why do you use a white tile
- it provides a constant white background
- for the indicator colour change to be seen more easily
why do only add 2 to 3 drops of indicator for every titration
- many acid or base indicators are weak acids
- so they have an impact on the end point of the titration
- this would cause inaccuracies if different volumes of indicator were used in different titrations for the same solutions
why do you fill the burette so that the gap between the tap and the tip is fiilled
- when the tap is turned on some of the solution in the burette will fill this gap
- meaning your initial reading is essentially wrong
- because some the of the solution will fill this gap and not enter the conical flask
how can you increase the accuracy of the reading of the meniscus
- by recording the burette to the nearest half a small division (0.05cm^3)
- using a light background to see the bottom of the meniscus
what do you do to decrease the chance of overshooting the end point
- add the acid solution from the burette steadily at first
- then much more slowly as the end point is approached
- then drop by drop when very close while swirling the flask
why do you stop adding solution form the burette just when the indicator changes colour
- to increase the accuracy of the titre
- adding any more solution does not change the colour any further
- but the accuracy will decrease
why should you repeat to obtain concordant results
- to increase the accuracy of your final calculated reading
- they should be within 0.2cm^3 of each other
why do you rinse the pipette and burette with deionised water and the solution to be used whereas the conical flask is only rinsed with deionised water
- because there would be an unknown amount of solution being titrated
- which would induce an error
what is the titre
the volume added from the burette during the titration
what is the end point and equivalence point and why should they coincide with each other
- the equivalence point is when the solutions completely neutralise each other or when the reaction is complete
- the end point is when the indicator just changes colour
- they should more or less happen at the same time or be as close as possible for your data to be accurate
what are concordant titres
- titres that are close together when you have repeated the titration
- usually within 0.2cm^3 of each other
